Recently, with development of technologies related to vehicles and increased consumer demand for low vibration and low noise, many efforts have been made to maximize riding comfort by analyzing noise, vibration and shocks that occur in a vehicle.
While the vehicle travels, vibration that occurs in a specific engine RPM range is transferred to the interior of the vehicle at a specific frequency via the vehicle body. At this time, the effect of combustion force of the engine on the interior of the vehicle is very large.
Vibration always occurs in an engine of a vehicle due to the structural features thereof, such as a periodic change in the center positions of a piston and a connecting rod due to vertical reciprocating motion thereof, an inertial force of a reciprocating part that acts in the axial direction of a cylinder, an inertial force of a connecting rod that shakes to the left and right of a crankshaft, and a periodic change in the rotational force that is applied to a crankshaft.
Therefore, in order to attenuate noise and vibration transferred from the engine and to support the engine, an engine mount is installed between the engine and the vehicle body. The engine mount is largely classified into a rubber engine mount, an air-damping mount, and a fluid-filled engine mount.
The rubber engine mount, which is formed of a rubber material, is very vulnerable to low-frequency and large-displacement vibration, and cannot sufficiently attenuate both high-frequency and small-amplitude vibration and low-frequency and large-displacement vibration.
Accordingly, a fluid-filled engine mount is being widely used, which absorbs and attenuates all vibration over a wide range, including high-frequency and small-amplitude vibration and low-frequency and large-displacement vibration, which are transferred to the engine mount by operation of the engine.
The fluid-filled engine mount is also referred to as a fluid mount or a hydro-mount, and has a structure in which damping force is generated as fluid encapsulated in the region below an insulator flows through a flow passage between an upper liquid chamber and a lower liquid chamber. Such a fluid-filled engine mount has an advantage of attenuating both high-frequency vibration (small-displacement vibration) and low-frequency vibration (large-displacement vibration) depending on the situation.
Recently, in order to improve the vibration-isolating performance of the fluid-filled engine mount, an active mount and a semi-active mount have been developed.
When the engine is idling, it is advantageous in terms of improvement of noise, vibration and harshness (NVH) performance to enhance vibration-isolating performance by reducing the dynamic characteristics of the mount. When the vehicle is traveling, it is advantageous to enhance the riding comfort performance by increasing a loss coefficient.
However, the currently developed fluid-filled engine mount has a problem in that the dynamic characteristics thereof and the loss coefficient are incompatible with each other, and thus, when it is intended to reduce the dynamic characteristics, the loss coefficient is reduced, whereas when it is intended to increase the loss coefficient, the dynamic characteristics are increased.
A semi-active mount (a switchable mount) has been developed in order to solve this problem. The semi-active mount is characterized in that when the engine is idling, the dynamic characteristics of the mount are reduced and in that when the vehicle is traveling, the loss coefficient is increased. Therefore, the semi-active mount is being widely used in vehicles.
However, the conventional semi-active mount needs to use a large-capacity coil so as to correspond to the rigidity of the rubber spring, and has a great number of parts, such as an actuator, and a complicated structure, resulting in a great increase in manufacturing costs and weight. Further, the conventional semi-active mount is larger than the fluid-filled mount (the hydro-mount), making it difficult to manufacture in a package.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.